One embodiment of the present invention generally relates to printers, and in particular, to a system and method for limiting unwanted ink penetration through an interface between a coverlayer and a flexible circuit to electrical traces of the flexible circuit.
One part during the manufacturing of an inkjet print cartridge typically includes adhesively bonding a thermal inkjet head assembly (THA) to the cartridge. The THA assembly typically consists of a semiconductor die, a flexible circuit and interconnect pads.
However, inadvertent bending and/or buckling due to structural thermal expansions and contractions can occur during adhesive sealing. For example, during heat, cure and cooling, the cartridge experiences thermal expansions and contractions. Consequently, these thermal expansions and contractions can cause buckling, bending and deformity to coverlayer structures.
The coverlayer is an adhesive layer that provides the bonding between the THA and ink cartridge. Typically, this is a sandwich type configuration with three layers of material. For example, a thermal plastic adhesive, such as a co-polymer resin, comprises the outer layers and a PET (polyethylene terephthalate) acts as the center core layer between the thermal plastic adhesive layers. The function of these layers is to provide protection to the flexible circuit and to bond the THA to the ink cartridge.
Ink that accumulates along the edge of the THA could penetrate through the interface of the coverlayer and THA to an active trace causing an electrical short. Since the coverlayer is a non-permeable material, the normal route of ink penetration is from the side of the coverlayer through to the edge of the ground trace and then to the active trace. Poor adherence of the coverlayer to the flexible circuit means poor circuit protection from ink penetration.
For example, if the adhesive failure causes coverlayer de-bonding from the flexible circuit, it can be exposed to the ink, which can cause the electrical short. Meanwhile, insufficient coverage of the coverlayer beyond circuit layout also means weakened circuit protection. This is because less coverage from the coverlayer leaves a shorter distance for the ink to penetrate through.
Unfortunately, typical printhead headland configurations, especially for smaller printheads, have limited space for coverlayer coverage. Further, electrical requirements do not allow the circuit to be trimmed any narrower to yield more space for extra coverlayer coverage.
The present invention includes as one embodiment a fluid ejection device for printing ink on a print media, comprising a flexible circuit with electrical traces, a coverlayer covering the electrical traces and adhering the flexible circuit to the fluid ejection device and at least one mechanical feature located on an outer edge of the flexible circuit near the electrical traces.
The present invention as well as a more complete understanding thereof will be made apparent from a study of the following detailed description of the invention in connection with the accompanying drawings and appended claims.